Fibrous dysplasia (monostotic), unspecified forearm

This code describes a benign, localized bone disorder where normal bone is replaced by fibrous tissue and immature woven bone, affecting a single bone in the forearm. This leads to weakened bone structure, which can result in pain, deformity, or pathological fractures.

Use this code when documentation specifies fibrous dysplasia affecting only one bone (monostotic) within the forearm, without further specification of laterality (left or right). This diagnosis is typically made based on imaging studies (X-ray, MRI, CT) and sometimes confirmed by biopsy.

• Ensure the documentation explicitly states "monostotic" and specifies the forearm as the affected site.
• If laterality (left or right forearm) is documented, use the more specific codes M85.031 or M85.032.
• Do not use this code if multiple bones are affected (polyostotic fibrous dysplasia) or if the specific bone in the forearm is identified.